Behind the scenes

JK Rowling's great-grandfather was also named Louis. It's unknown whether Louis Weasley is named in honour of him, though.

Etymology

The name "Louis" is the French form of Ludovicus, the Latinized form of Ludwig. This was the name of seventeen kings of France, starting with Louis I the son of Charlemagne, and including Louis IX (Saint Louis) who led two crusades and Louis XIV (the 'Sun King') who was the ruler of France during the height of its power, the builder of the Palace of Versailles, and the longest reigning monarch in the history of Europe.